Radio locator test apparatus



Apri! 27, E948. E. L.. GiNzToN 2,440,26

l RADIO LOCATOR rEsT APPARATUS Filed May 30, 1945 4 Sheets-Sheet 1 fao /39 TEST ,4MM/M705 ATTORNEY W nu ww rm April 27, i948.

2000 CYCL E E. l.. GlNzToN RADIO LOCATOR TEST APPARATUS Filed May 30, 1945 INVENToR Eon/,4R0 ,6. 'm/ZTo/v pn'ii 27, E948. E. L. GlNzToN 2,440,261

RADIO LOCATOR TEST APPARATUS Filed May 30,- 1945 4 Sheets-Sheet 3 @LMA 7 394 E. l.. GlNzToN E RADIO LOCATOR TEST APPARATUS Filed May so, 1945 4 sheets-sheet 4 t z L I Illu VMA/wwa R 1 l Q s bo Q .J N A J w Q pq me t \`f: *E

SX .a v u@ E 1 R4 INVENTOR ATTORN EY Patented pr. 27, M

RADIO LOCATOR TEST APPARATUS Edward L. Ginzton, Garden City, N. Y., assigner to The Sperry Corporation, a corporation of Delaware Application May so, 1945, serieu No. 596.701

Claims. 1

This invention relates to testing apparatus and electronic circuits. This patent application is a continuation-impart of patent application Serial No. 472,794, filed January 18, 1943, now abancloned.

An object of the invention is to provide apparatus for testing electronic circuits and cathode ray devices, e-specially locating devices of the search or scan type employing transmitted and reflected radio waves.

A specific object of the invention is to provide apparatus for testing object locators of lthe Azimuth-Search type, which project a beam of ultra high frequency radiation in pulses toward the horizon, and oscillate the beam through a predetermined angle of azimuth, to scan the horizon and thus search for objects which may be invisible-but which intercept the projected beam. In case such an object intercepts the projected beam, the beam is reiiected and received by the locator. The azimuth of the detected object is indicated by the azimuth of the projector when the projected pulse is intercepted and the range of the detected object is indicated by the time interval between the transmission of the pulse and the reception of its reflection.

These indications are produced graphically by a cathode ray oscilloscope including a cathode ray tube having a deflecting beam, a pair of sweep circuits and a control electrode. The cathode ray oscilloscope beam is deflected horizontally by a triangular wave caused to rise substantially linearly to represent azimuth as the projector is rotated in azimuth. The cathode ray oscilloscope beam is also deflected vertically by a saw-tooth wave representing time duration and therefore range. However, the cathode ray oscilloscope beam is usually held on? by its control electrode so that nothing appears upon the cathode ray oscilloscope screen until a reflected pulse is received. The pulse receiver is arranged to energize the cathode ray oscilloscope control electrode upon reception of a reflected pulse so that a spot is produced on the cathode ray oscilloscope screen, the coordinates of which indicate azimuth and range of the detected object or target.

Such locators are intended primarily for locating moving targets from a moving station, such as an airplane. They must function with precision and reliability and yet often cannot be tested under actual operating conditions irrimediately before being placed in use for their intended service. A test at this time would be highly desirable, since the aircraft on which the locatore are mounted must be stored and may have been 2 subjected to adverse conditions during transpor-4 tation before arriving at the scene of action.

It is accordingly a further object of the invention to provide a synthetic test for such locators, which may be applied Without actually generating or reflecting the ultra high frequency energy pulses employed in actual operation of the apparatus.

Other and further objects and advantages will become apparent as the description proceeds.

In carrying out the invention in its preferred form, a vacuum tube circuit is provided for generating voltages simulating the voltages normally produced by the'detector of the receiver due to the radio locator pulses and for synchronizing such simulated voltages in any desired phase or timing relation with the horizontal deflection triangular wave, to vary the azimuth-representing position of the spot. Adjustments are also provided for simulating any desired range or any pulse reection factor, in order to simulate al1 conditions under which the locator may be used and enable the tester to determine whether the locator indicates correctly on every part of its screen.

A better understanding of the invention Will be afforded by the following detailed description considered in connection with the accompanying drawings, and those features of the invention whichA are believed to be novel and patentable will be pointed out in the claims appended hereto.

In the drawings,

Figs. lA and 1B are schematic or block diagrams of one embodiment of this invention;

Fig. 2 is a schematic diagram and graphic explanation of the manner of operation of a radi locator to be tested;

Fig. 3 is a circuit diagram of the test apparatus of Figs. 1A and 1B;

Figs. 4A and 4B are graphs illustrating the output Waves of a multivibrator unit forming an element of the apparatus of Figs. 1A, 1Bvand'13 Figs. 5A and 5B are graphs illustrating the result of differentiating the output waves of Figs. 4A and 4B;

Fig. 6 is a graph illustrating simulated pulses produced by the apparatus; and

Fig. 'Isis a fragmentary circuit diagram of a modication-in-part of the apparatus of Figs. 1A, 1B and 3.

Like reference characters are utilized throughout; the drawings to designate like components of the apparatus. v

A radio locator of the type which may be tested by applying simulated pulses in accordance with as including a directive antenna |51 pivoted fori.

oscillation about a Vertical bearing |158.v and ldriven through a coupling rod |59 by a crank |65 rotated,

as through a worm and gear-system,.by-a-motor |6I. A potentiometer |63 supplied with potential by battery |64 mat7 be connected mechanically to the antenna |51 and lelect rically,to the` horizontal sweep terminals of the oscilloscopeY |56, for applying to theoscilloscope terminals -avoltage varying substantially according to the azimuthal displacementof. the antenna I5 1,from a neutralposition.. The .motor drive system |59, |60., ISI. may be. so arranged. as to drive the antenna. |51. atsubstantiallyuniform .angular speed, so..that a nearlytriangular azimuth sweep electricwave is produced` The transmitter. I52land the receiver |54 may be coupled to the antenna |51 through ultrahigh frequency. energy conductors .suchas hollow-.pipe

waveV guides orcoaXial transmission,lines. A transmit-receive selective energy transmission deviceISof thelionizable. gas-.lledresonator type, commonly referredto asa T-Rbox, may be connected inthe Aultra high frequency transmissioncircuitto the receiver. |54, for. freelypassing low` intensity energy. intercepted. bythe antenna |51, to the, receivenliliand.orgreatly attenu ating thehigh. intensity, energy pulsesI supplied by -the transmitter |52,y toiaord. some lprotection ofthe receiver |5421.: A` generally'similar protective device, |66, referredto. asa lt-,'I4 box, may be coupled tothe ultrahigh `frequency energy. .conductor. connectedsto the ,transmitter |.52.,for furtherV regulating the.. distribution of. Athe output energy from transmitter |52 and the energyinterceptedby antennaVA |51'.V The 4'IL-Ribox `|65 and the bOX, c I 5 5; arewell-kilollvn, devices .for the purposes setiorth abbi/aand hence need not be discussed here in greater detail.

The receiver, |54.;may.be of; the superheterodyn@ type, anlzmay be ,arranged to. provide at terminals |68 a detected version` of the ultra nigh frequency-energy. received; through. the 2u-R box |65; yThese detectedisghalsmay befalpled tothe inpututerminals. of a; gating circuit |55, which isrconnectedto the pulse generator lesto receive timing signals therefromand to pass to a pair of outputterminals only those detected signals vfrom the receiver |54 which, occur inthe intervals betweenA the 4timing signalsl from the pulse generator |53,v The, output terminals of the gating circuit |55are connectedtozthe control grid circuit of the oscilloscope |55, insuch a wayas to produce ,a variation of thebrilliance of the fluorescent spot on the screen of the oscilloscope at the instant AWhen a detected p ulsel from receiver |54 is passed;V through thegating circuit In accordance with the present invention, test apparatus indicated schematically at |39 is connectedto-tcs tterminals,3,5, 3| and4 I'lIl fortest operation of the-V gating. circuit |55.' and the oscilloscope |56, and, if desired, for generating a triangular azimuth sweepvoltage simulating the voltage normallygproducedbythe; movement of acidacl the antenna system I5| including potentiometer |63 and battery |613. The test apparatus |39 may be connected to terminals 3U to receive or supply the triangular-wave horizontal sweep voltage corresponding to movement with the antenna |51 of the potentiometer |63; to terminals 3| for applying thereto a voltage simulating the detected output voltage of receiver |54, and to terminals III for Synchronizingrthe voltage applied to terminals 3| with a vertical sweep saw-tooth wave oscillator which forms a part of oscilloscope 56.

The radio locator I is represented functionally in Fig. 2. One of the elements of the oscilloscope |,56'is,.afcathode ray tube I2 having a conventionalgelectron.gun I3 for producing a cathode ray beam I4- impinging on a iiuorescent screen I5., The electrongun I3 includes a conventional control electrode or grid I6 by means of which the beam. I4 may be either cut off or permitted to impinge on screen I5, ,according to the voltage applied to. the control electrode.

'Ijliecathoderay-.tubeI2 is so mounted that a face vieviV of, itsscreen |5appears behind a calibrated transparent chart I1; CoordinateV lines which actually appear on the chart i1 are shown in Fig. 115,` but are, omitted in Figs, Maand 2 for clarity. AAt thepointlon the chart Il'where the cathode ray beamA irrimpinges V4en the screen I5 a spot |3- appears, unless-the beam- It` is cut off. The cathode ray tube I2 incl-ud'es'apairof deflection circuits (notrshown) for causing the spot I8 to move along two mutuallyvperpendicular axes.

A4 currentorvoltage of triangular-Wave shapel I 9 isi` applied to onedeii'ection circuit for causing horizontal-deilection ofthe beam I8'to represent variationsin azimuth of the position ofan energyreiiecting. target, anda voltage orcurrent having a .saw-tooth wave shape 25a-is applied to the other-deflection circuit'for causing vertical deiiectionfof-fthe spot. I8Y to representy range. The frequencyofVthe-,Wave-iIais relatively slow, for example-oney cycle per second, and is produced by suitable. mechanism within vthe radioY locator I |sucl1 as the. sliding brush potentiometer |63. The frequency of the. saw-toothwave- ZDfis high in comparison fwith. that of the `.wave I9, for example 2,000. cycles per second. i This wave also is producedby, suitable mechanism such as a sawtooth -Wave electronic` circuitY within theY radio locatorIfI.

As` represented bythe guide lines I9! andl 20 in Fig.2, the instantaneous. position of-.the spot I8Y relativetothe 4chart I1 depends upon the instantaneous magnitudes. of thefwaves I9 and 20, at ,the time whenV thev cathode-ray control grid voltage is such avalueas to `permit.theelectron beam .to impinge onthe fluorescent screen.

Normally, however, thefspot I8 does-not appear on Athe, screen. or chart because thecathode-ray tube. control .-grid'is normally biased` t0-cutvoff the. electronbeam.Y For this purpose, a cut-oli bias. ,device` represented` by i the f rectangleY 2 I (Fig. 2) vis,,provided .having` anelectrical COIiDBCtion or a coupling. to the,control gridf- I6.

The radio-locator. II -in normal use-radiates recurrent pulses, of ultra high frequency energy, as, the ,antenllafll -moves from side to side to vary the'azimuthal directivity of the radiov object locat0r,. Thereceiver |54 produces a series of recurrent pulses, due to detection of a small portionoi" the'transmitteroutput energy,. and also produces certain additional output pulses varying in strength according to the strength of reiiected ultra high frequency energy vreceivedfrom distant objects, and varyingin chronological relation to aaioem the wave I9 and recurrent receiver output pulses according to the azimuthal direction and the distance, respectively, of an energy-reflecting object. Such pulses are represented in Fig. 2 by the series of vertical lines of the graph 22. Each of the equally spaced vertical lines 24, 25, 26, 21, 28, etc., in the graph 22 represents the receiver output resulting from one transmitted pulse. A receiver output pulse 29, due to detection of energy reflected from a distant object, is illustrated as occurring between recurrent pulses 26 and 21. For illustrating such a reected pulse more clearly, the center portion of the graph 22 including the vertical lines 24, 25, 26, 21 and 28 and the reflected pulse line 29 has been represented as magniiied within the circle 23. The reflected pulse 29 is shown somewhat shorter than the pulse 26 to indicate the absorption of energy and loss resulting in the transmission and return to the radio locator The horizontal spacing between the transmitted pulse 26 and reflected pulse 29 represents the time required by the pulse to travel the distance to the target and back. This time interval is relatively short, being between a microsecond and 500 microseconds. The gating circuit |55, which passes to the oscilloscope |56 the pulses received during the intervals between the uniform recurrent pulses of the transmitter, is responsive to pulse 29, and permits this pulse to overcome the control grid bias in the oscilloscope and to permit the spot I8 to appear thereon.

The saw-tooth wave 29 generated in oscilloscope |56 is synchronized with the pulses generated by the pulse generator |53. Since the instantaneous voltage of the saw-tooth wave 2|) increases progressively with time, its voltage at the instant of reception and detection of pulse 29 is proportional to the time delay between the immediately preceding transmitted pulse 26 and the reflected pulse 29, and the vertical coordinate of the spot |8 therefore represents the time required for the pulse to be transmitted and reiiected, or the range of the target. Since the target is intercepted only when the microwave projector is directed along the azimuthal direction of the target, the horizontal coordinate of the spot I8 represents the azimuth angle of the target. Accordingly, the appearance of the spot I8 on the cathode ray tube indicates the presence of the target and the location of the spot relative to chart |1 indicates the azimuth angle and range of the target.

In order that such a radio locator may be tested without the necessity for actually produc-- ing a projected microwave beam and actually intercepting it by a target, means are provided for simulating the pulse voltages, represented in the graph 22 and shown magnied within the circle 23 of Fig. 2, and means may also be provided for simulating the azimuth sweep voltage wave I9,

l or for making use of the apparatus within the locator for obtaining such a triangular wave azimuth voltage and synchronizing the simulated pulses therewith.

In the apparatus illustrated in Fig. 1B, such an azimuth voltage is assumed to be available and to appear at a pair of terminals 30 within the radio locator. The locator is shown equipped with a pair of signal input terminals 3| to which simulated pulses may be applied by test apparatus |39, and with a further terminal pair 1| at which synchronizing voltage from the pulse generator |53 is made available for synchronization of the test apparatus |39. The apparatus is made adjustable so that a simulated reected pulse may be produced at any angle of azimuth. Any desired delay of the reected pulse relative to the recurrent pulses and, similarly, relative to the saw-tooth wave 20, may be produced to represent a desired target range, and any desired degree of attenuation of the reflected pulse with respect to the transmitted pulse may be produced. In this manner, the radio locator I may be tested under a condition simulating the operation of receiver |54 when detecting a target appearing at any azimuth direction, at any range, and under any assumed condition of reflected wave intensity.

The embodiment of the invention illustrated schematically in Fig. 1B comprises va double dif-- ierentiator 32 for converting the triangular wave azimuth voltage at the terminals into a series of spikes which will have a frequency of one cycle per second if the azimuth voltage has this frequency, an adjustable repeating multivibrator 33 adapted for synchronization with the vertical sweep voltage circuit of the oscilloscope |56, a pulse generator 34 for converting the voltage variations produced by the multivibrator 33 into voltage spikes simulating pulses received by the radio locator in practice, a single-pulse multivibrator 35 synchronized with the output of the double differentiator 32 for producing an adjustable time delay for representing variations in azimuth, and a second single-pulse multivibrator 36 having a small time delay of the order of 500 microseconds for preventing the production of a simulated reilected pulse in the pulse generator 34 except when the device 36 is triggered by the output ofthe single-pulse multivibrator 35.

The double differentiator 32 has input connections 31 connected to the azimuth voltage terminals 36 of the radio locator |I and has output connections including the connection 39 to the input of the single-pulse multivibrator 35 for synchronizing the device 35 with the azimuth voltage at the terminals 3B. For isolating the devices 32 and 35, a buler 40 is preferably interposed between the synchronizing input connection 39 and the single-pulse multivibrator 35. Likewise, a second buier 4| is preferably interposed between the single-pulse multivibrators 35 and 36.

Any desired means for making the multivibrators 33 and 35 adjustable may be utilized, but for the purpose of illustration the multivibrator 33 is shown as having a potentiometer 42 for making it adjustable and the multivibrator 35 as having a variable condenser 43 for making it adjustable. The internal connections of these devices will be described more in detail in connection with the description of Fig. 3.

The pulse generator 34 includes two stages having a common output connection 44 coupled through a coupling condenser 45, for example, to one of the signal input terminals 3| of the radio locator The return connections may be through ground, as represented in the drawings. The two stages of the pulse generator 34, represented in Fig. 1B by the half rectangles 4S and 41, have separate input connections 48 and 49, respectively, leading from two different output terminals or stages of the multivibrator 33. One of the stages of the pulse generator 34, namely, the stage 46 for producing the simulated transmitted pulse, may have a xed bias. However, the other stage 41 for producing a simulated reflected pulse has a connection represented by a resistor 50 for normally biasing the 9 tube 41 is responsive to the second peak, which is the positive peak of the wave 84, since the wave 84 is derived from the negative rectangular wave 19. Since the pulse generator 34 is of the cathode follower type, its output wave appears at the common cathode connection 85.

For adjusting the height of the pulse pro- Y 89 to the negative terminal of the C battery 86 I and the magnitude of the bias voltage provided by source 86 is made great enough for normally biasing the ltube 41 so far beyond cut-orf that it is not responsive to the positive peaks of the input wave 84, unless a bias-reducing voltage is supplied by the single-pulse multivibrator 36,

The output wave 55 of the pulse generator 34 appears across the common cathode resistor S2. For adjustment of the height of the first spike 54 simulating a transmitted pulse, the tapped potentiometer 81 is provided, and for adjustment of the height of the spike 56 representing the reflected wave, the voltage output of the singlepulse multivibrator 36 is made adjustable in a manner to be described hereinafter.

The buier 40, as illustrated, comprises a triode vacuum tube connected as a cathode follower having a control electrode 9|. 'Ihis is capacitance coupled through the conductor 39 to the output of the double diierentiator 32. There is a cathode resistor 92 with an output connection 93 from the cathode of the tube 40.

The single-pulse multivibrator 35 comprises a pair of triodes 94 and 95 with direct resistance coupling between the tube 94 and the control electrode 96 of the tube 95. If desired, the coupling resistor 38 may be by-passed by a capacitor. For adjustment of the length of the square wave output or the delay provided by the circuit, an adjustable capacitance coupling 43 is provided between the tube S5 and the control electrode 91 of the tube 94. Such adjustable `coupling may be provided by means of a variable capacitor or a bank of capacitors S8 having diierent capacitances, any one of which may be selected by means of a selector switch 99. To insure termination of the oscillation of the multivibrator 35 after a single pulse, the control electrode 91 of one stage 94 is positively biased by connecting its grid-leak resistor IDI to the positive terminal |02 of the anode supply source |03. Furthermore, the control electrode 96 of the other stage 95 is negatively biased by connecting its gridleak resistor |54 to the negative terminal oi a source of bias voltage such as a C battery |95 having its positive terminal grounded. For triggering the single-pulse multivibrator 35 from the output of the buffer 40, a cathode resistor |56 is provided in series with the cathode connection of the tube 94 and thecathode |01 is coupled by a coupling capacitor |58 to the output lead 53 of the buffer 40. The lead 93 may also be coupled by a second coupling capacitor |58' to the control electrode 96 of the tube 55.

The arrangement is such that the tube 95 is normally non-conducting and, therefore, a negative rectangular wave 51 appears at the anode 10 of the tube v whenever the single-pulse multivibrator 35 is triggered. This negative output is coupled to the control electrode `|09 of the buffer 4I by conventional small-time-constant resistance-capacitance coupling serving as a differentiator and the buier 4| is arranged as a cathode follower stage having a cathode resistor H0 and an output connection connected to the cathode end of the resistor l I9.

The single-pulse multivibrator 36 also comprises a pair of triodes ||2 and H3, th'e former of which is positively biased through a grid-leak resistor |14, which is made adjustable to permit adjustment in the length of the square wave output 59. The other triode l |3 is negatively biased by means of, a conventional negative bias source such as a C battery l5. Although the single-pulse multivibratorf 56"is"similar in its connections to the single-pulse multivibrator 35, the time constantsA are verymuch dierent. Th'e time constants of the coupling circuits Aofthe single-pulse multivibrator 35 are so chosen that the variation of coupling capacitance by selection of different capacitors by the bank 98 permits variation in the length of the rectangular wave 51 from a fraction of a second to nearly a second, assuming that the apparatus is to-bevused in' connection with the testing of a radio locator having an azimuth wave |9 with a frequency oi one cycle per second.

` The time constants vof the single-pulse multivibrator 36 are so chosen, however, that the length of the positive squarewave 59 appearing at the anode of the tube H2 is of the order of 500 micros'econds. n

The square Awave output 59 o f the single-pulse multivibrator 36v is taken from the anode of the tube ||2 and-applied throughan adjustable resistor ||6 to a point ||1 in the control electrode circuit of the tube 41 of the pulse generator 34. The constantsare so chosen that the tube 41 is normally biased further beyond cut-01T than theheight of thep'ositive spike of its input wave 84, and the appearance of the rectangular wave 59 reduces the negative bias suciently so that it is made a fraction of the height of the positive spike of the input wave 84 of the tube 41, Adjustment of the resistor ||6 permits adjustment of the positive voltage introduced in the negative bias 'circuit of the tube 41; and therefore permits adjustment of the reduction in bias so that height of the second spike 56 in th'e wave 55 simulating a re'iiected pulse may be adjusted to represent variations in absorption of the actual reflected pulse. y

The output waves of the multivibrator 33 and the pulse generator 34 are illustrated more exactly in Figs. 4A to 6. In these gures, voltage is measured in the vertical direction and time in the horizontal direction. Thus, Fig. 4A illustrates the' positive rectangular Wave shape appearing at the anode ofthe tube 15. A dotted portion I8 of th'e rectangular wave 18 represents variation in length (or time duration) of the square wave which may be produced by varying the relative length of conducting periods of the tubes 14 and 15 by adjustment of the tap 11 on resistor 15. Corresponding negative square waves 19 appear at the anode of the other multivibrator tube 14, :and a corresponding adjustment in length of the square wave represented by the dotted line |9 is vpermitted by adjustment of the tap 11.

Die'rentiation ofA the square waves 18 and 13 is represented in Figs. 5A and 5B. The time intervals between the positive and negativespikes of the waves' 83 and B4 shown in Figs. 5A and 5B may be,y adjusted by adjustment ot the'taplrl so as to correspond. toY the lengths-of: the square waves 'I8 and' T9. For exampler referring; to-Fig. B, the time intervalx betweenthe negativespike |20- andl the positive spike |2| maybe adjusted inA the manner just described..- The negative spike' |253` occurs at th'esame instant-as the positive spike |22 ofthe wave 83 Vshown in. Fig.. 5A. Since the pulse generator tubes, I6v and M. are responsive only to positive input.v voltages,Y the tube 46 will be responsive tot the. positive vspike |22 of the wavef83 and the tube d-'twillfbe'responsive to the positive spike' I2I or the` wave 84a Accordingly,l ifY both: positive spilites'tl and I2-I- are permitted to appear at the=y respective controll electrodes ofthe tubes 46 and 47|Y a double spike output wave 55, shownainFig. 6', willl appear across the cathode resistor 82 of thefpulse' generator 34.

.The spacing between the-instiand secondspikes 54 and 56 will bel determined; by the spacing betweenthe positive spikesl |'22 and |-2| ofthe-waves 83 andSt, respectively, and' tl-iereiore` may be' adjusted by adjustmentofl the tapf'lf'lfl in the-multi-` vibrator 33. Normally,however',4 the controlelectrode of the pulse generator tube ilI isbiase'd. far beyond cut-oil andthe second spike` Sii-does not appear in the outputwave55,` asindicatedfby the dottedrepresenta-ti'on 5B' in Fi'g.` 6.

The Voltage outputV of the single-pulse. multivibrator 36 is such that the. negative bia-s of the tube 41 is reduced toa value suchl asrepresented by the arrows |123 in Fig.- B-'for example,` which permits the-second spike 56 to' appear in the=wave 55 but to have a smaller magnitude thanl thefrst spike 9c. Adjustment off-,the remaining negative bias I 23l of the tube 41 by' adjustment of the resistor H6 in the single-pulse-,multivibrator 3E' permits adjustment of the h'eig'ht of the second pulse 5t. The length of the square wave output Si` of the single-pulse multivibrator 36 is made sufficient so Vthat it willf permit appearance of the second spike 'in-the wave ifwhen desired, regardless of the vsetting of the.' tap 11 determining the length of the square wave'si 181 and 12J.' Obviously, the length of th'eI WaverB-S need. be no greater than the interval between successive square Waves T8 or 19.

When 4an operator wishes to test' the radio locator H by means` of testing apparatus. of the type just described, the input terminals 3T of the test apparatus are connected tothe azimuth voltage terminals 30 of the radioY locator I; the synchronization termin-als |4001' the test apparatus are connected to the corresponding :terminals |1| of the radio locator; and the signal-output terminals 3| of the test apparatusV are connected to the signal terminals 3| of the radio locator I The potentiometer l2V is adjusted to represent variations in range iin :order to cause the spot I8 to appear at different heights relative to the chart Il andv the selector switch 99 is adjusted to represent variations 4iri azimuth and cause appearance'of the spot |8 at vari-ous positions in a horizontal direction along the chart I1. order to represent the variations in absorption of the reflected wave causing 'variations in height ofthe reiiected wave representation 29 (Fig. 2) the resistor iIS in the single-pulse multivibrator 3G is adjusted. Thus, the response of the radio locator to the various indications which it may be expected to receive in' practice will be determined, and any defects in the apparatus ,or any regions. of the chart in which the indication is indistinct' maybe ascertained before the radio locator YI| isv placed in actual service.

Inasmuch as the repetition rate ofV the pulses is. ordinarily very high in relationfto the frequency of the azimuthsweep in object locators off the Azimuth-Searchtype, for. example, in the ratio 2,000 to 1,. it. is not-necessary in such cases to provi/de any means of synchronizing the simulated pulses with-the azimuth sweep;

In the-apparatus thus far described, it has been assumed that the azimuth voltage I9` is to be taken from the radio locator Il. However, if desired, the azimuth voltage may also be simulated by thetest apparatus, so that the antenna |57. need not be driven. by the motor I'l for the test. For this, purpose. an additional multivibrator stage |21!` illustrated in Fig. 7 may be included. in. the test apparatus |39. This multivibrator stage is similar in connections and principle of operation to the multivibrator 3.3' described4 above. The multivibrator |25', however, hassuch time constants that it producesa rectangular output wave IZwhich has a frequency ofone cycle per second, assuming that a one-cycle-per-second azimuth Wave I9A is tdb'e simulated. For converting the square wave-[25-Y intoA a substantially triangular azimuth wave 52', an integrating circuit is provided consi'sting. of a resistor |26v and a capacitor |21 in series connected across the second tubel |28 of. the multivibrator |24.. The triangular WaveV appears across the capacitor |21- and. isV applied to the azimuth sweep wave terminals 3i] to produce an azimuth sweep since it is assumed that the azimuth voltage is to be supplied externally. In this case, the, double dnerentiator 32y of Figs. 1B and 3 is not neededr and synchronizing. pulses are taken from the anode of the tube |28 of the multivibrator |24' through a differentiating circuit comprisingV a capacitor |29 and a resistor |30 connected in series across the tube |28, the synchronizing pulses 53 then appearing acrossl the resistor |30. The junction terminal, |3| of the differentiator |29|3il may be connectedto the controll electrode 9|- of' the buier tube 4G shown in Fig.. 3. The butter tube 4.0' is inv turn coupled to the tubes 94 and 95 of the single-pulse multivibrator 35 of Fig. 1B, as illustrated in detail in Fig. 3, Iand the. remainder of the apparatus may be as illustrated in Figs. 1B and 3.

As manychangescould be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description o1' shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Apparatus for producing simulated pulses for testing' a recurrent-pulse radio locator having azimuthsweep voltage wave terminals and including a directional pulse projector periodically sweeping through a range of directions, said apparatus comprising a pair of input terminals for connection to the azimuth sweep voltage wave terminals of said radio locator at which a triangular sweep voltage wave appears having a frequency corresponding to the directional sweep frequency of the pulse projector of said radio locator, a double differen-tiator for forming from such a tri-angular sweep voltage wave synchronizing spikes of the same frequency, a two-stage repeating multivibrator circuit having an adjustment for permitting variation of the ratio of on and off periods of one stage of the multivibrator with respect to the other, said multivibrator having a frequency corresponding to the repetition yrate of recurrent pulses of s-aid radio locator, a pair of diierentiators connected to oppositepolarity output terminals of said multivibrator, -a two-stage pulse generator having one stage connected to one of said difierentiators and the other stage connected to the other of said differ- ;entiators, said two stages having common output terminals and having means for normally biasing one stage of the pulse generator sufficiently beyond cut-oir .to prevent response to input diierentiated waves, a first single-pulse multivibrator synchronized by said synchronizing spikes and having an adjustment to permit variation in delay of the order of the period of an azimuth wave used in said radio locator, a second single-pulse multivibrator arranged yto be triggered by the output of said rst single-pulse multivibrator and having a pulse duration of the order of the interval between pulses produced by the radio locator to be tested, and an output connection between said second single-pulse multivibrator and the bias circuit of said one stage of said pulse generator for rendering said one stage .of the pulse generator effective for 4the duration of the output wave of the second single-pulse multivibrator, whereby simulated transmitted pulses are produced in said pulse generator and a simulated reected pulse is produced therein .occurring at an instant in relation to the azimuth sweep voltage wave determined by the adjustment of the iirst single-pulse multivibrator and having a range-indicating delay determined by the adjustment of the repeating pulse multivibrator.

2. Recurrent pulse radio locator testing apparatus comprising a unit for producing a triangular directional sweep voltage wave, a unit for producing square waves with a repetition rate corresponding to the repetition rate of the recurrent pulses of the radio locator, apparatus for converting said square waves into pairs of positive spikes with means for normally suppressing the second of each pair of spikes, an adjustable delay device supplied with said triangular sweep Voltage wave for producing an output voltage having adjustably delayed discontinuities, and a unit triggered by the output Voltage of said delay de- Vice for momentarily overcoming the suppression of said second spike, whereby simulation of variations in radio locator target range may be produced by variation in length of the square waves produced by said square wave device, and variations in radio locator target direction may be simulated by adjustment of the delay device to determine the time instant in relation to the directional sweep voltage wave at which the second spike of one of said pairs of spikes is permitted to appear unsuppressed.

3. Recurrent pulse radio locator testing apparatus comprising a unit for producing square waves with a repetition rate corresponding to the repetition rate of the recurrent pulses of the radio locator, apparatus for converting said square waves into pairs of positive spikes with means for normally suppressing the second of each pair of spikes, and a unit for overcoming the suppressing of the second spike of a selected pair of spikes whereby pulses transmitted by said radio locator are simulated by the rst spike of such pairs of spikes and the reiiection of one of said pulses is simulated by the second spike of said selected pair.

4. Recurrent pulse radio locator testing apparatus comprising an adjustable unit for producing square waves with a repetition rate corresponding to the repetition rate of the recurrent pulses of the radio locator and with adjustable time duration of said square waves, apparatus for converting said square waves into pairs of positive spikes with means for normally suppressing the second of each pair of spikes, and a unit for overcoming the suppression of one of said second spikes whereby simulation of variations in radio locator target range may be produced by variation in length of the square waves produced 4by said square wave device, the iirst spike of each pair simulating a pulse transmitted by said radio locator, and the unsuppressed second spike of a pair simulating a reflection of a transmitted pulse from a radio locator target.

5. Recurrent pulse, periodically direction-varying radio locator testing apparatus comprising a pair of input terminals for connection to a source of a triangular electric wave corresponding to the periodical directional variations of the radio locator, means ior producing pairs of positive pulses having a high repetition rate in comparison with the frequency of said triangular electric wave, adjusting means for varying the time interval between the pulses of each pair, means for normally cutting off the second pulse of each pair, an adjustable time delay device responsive to said triangular electric wave and synchronized therewith, and means triggered by said time delay device for counter-acting said pulse-cut-off means and permitting the production of the second pulse of a pair for simulating a reiiected pulse at a time in relation to said triangular electric wave determined by the setting of said adjustable time delay device.

6. Apparatus for producing simulated pulses for testing a recurrent pulse radio locator producing an electric azimuth sweep signal, said apparatus comprising a unit for producing square waves with a repetition rate corresponding to the repetition rate of the recurrent pulses of said radio locator, said rate being high in comparison with the frequency of the electric sweep signal, apparatus for converting said square waves into pairs of positive spikes with means for normally suppressing the second spike of each of said pairs of spikes, an adjustable delay device with means receiving said azimuth sweep signal and synchronized therewith, and a unit triggered by said delay device for momentarily overcoming the suppression of said second spike, whereby simulation of variations in radio locator target range may be produced by variation in length of the square waves produced by said square wave device, and variations in radio locator target azimuth direction may be simulated by adjustment of the delay device to determine the time instant at which the second spike of a pair is permitted to appear.

'7. Recurrent pulse radio locator testing apparatus comprising a pulse generator for periodically producing pairs of pulses at a rate corresponding to the recurrent pulse repetition rate of the radio locator, means connected to said generator for normally suppressing the second of each pair of pulses, and a, unit for periodically overcoming the suppressing vof said second pulses whereby transmitted pulses of said radio locator are simulated by the lrst of each pair of pulses and reflections of some transmitted pulses are simulated by said unsuppressed pulses.

8. Radio locator testing apparatus as dened in claim '7, including means for adjusting the time period between pulses in each'pair to simulate variations in radio locator target range.

9. Recurrent pulse periodically scanning radio locator testing apparatus comprising a, pulse generator for periodically producing pairs of pulses at a rate corresponding to the 'recurrent pulse repetition rate -of the radio-locator, means connected tozsaid generator for normally suppressing the second of eachpairof pulses, a unit coupled to said radio locator land lcont-rolled synchronously with the scanlingiof said radio locator for periodically overcoming ythe suppressing of said second pulses, and ,delaymeans in said unit for adjusting the =phase relation of the operating period ,of said -unit with respect to said scanning whereby transmitted pulses of Vsaid radio locator are simulated -by the first ,of Aeach pair of pulses and reections of some transmitted pulses are simulated by said unsuppressed pulses.

19,. Apparatus for testing -a radio locator having fa cathode-'ray oscilloscope including a horizontal -deiection circuit anda vertical deection circuit, a sweep Voltage generator Vof -a rst frequency coupled to said horizontal deflection circuit, asaW-tooth wavegenerator coupled to said vertical deflect-ion Vcircuit and arranged for eX- l ter-nal synchron-ization with recurrent pulses Vof a second frequency appreciably greater than said rst frequency, and means for receiving recurrent pulses of said second frequency for synchronization Aof gsai-d saw-tooth Wave generator and receiving :occasional pulses during intervals between said `recurrent :pulses and selectively applying said occasional vpulses to said oscilloscope to produce abrupt `variaticms of "brilliance thereof in-accordance With-said occasional pulses; said testing apparatus comprising: rst multivibrator means responsive to the horizontaldeection Vvolgtage generator vfor producing Xed-duration -voltage impulses ysynchrcmized therewith in l.adjustable Lphase relation, second multivibrator means for generating a'rstyseries of recurrentpulses at said second frequency for synchronization with the vertical deflection saw-tooth Vgenerator and for :generating a -second ser-ies of recurren-t (pulses at sa-id second frequency adjustablyspaced'from said rst pulses, means responsive 'to said first multivibrator mea-ns and operatively Vcoupled to said secondmultivibrator-means for selecting :the pulses of :said second series Vcoincident with said fixed-duration voltage-impulses and blocking the remaining 'pulses of said second series, and means for applying said -rst series recur-rent 4pulses and the selectedfpulses of said second ser-ies to the pulse freceivi-ng means of the radio locator.

EDWARD L. GINz'r-ON.

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